Wire a fan to a separate controller in bathroom

[viewer]

Sorry, but for that money you won't get a good humidity-controlled fan. Separate humidistats (like this http://www.xpelair.co.uk/xrh-remote-humidistat.html) work well, but are not cheap and, of course, need wiring which may be physically difficult. You could check the dewpoint using (http://www.amazon.co.uk/s/?ie=UTF8&keywords=dew+point&tag=googhydr-21&index=aps&hvadid=17221189910&hvpos=2t2&hvexid=665510&hvnetw=s&hvrand=16703520441635468171&hvpone=&hvptwo=&hvqmt=b&hvdev=c&ref=pd_sl_41rzfyx9v), but again you're spending money.
One thought on your comments about the bedroom wall - the mould starts at the bottom and moved up? This sounds odd, usually you'd expect it in the corners at the top at first (especially behind furniture). Have you checked the outside wall and rainwater goods? The water from a gutter running down a wall may not penetrate but can super-cool the wall.
HTH

 

[dgardn2012]

I may leave off changing the fan, and get a decent one down the line. I will stress to the new tenants that if they don't want the light, on to open the window a bit. The mould on the wall was in the corners, but where there bed was it was close to floor, but worse the higher it got. The ceilings are sloped and again, it started in the corners and went across, probably because i have loft insulation the main ceiling was unaffected, but there was no way of insulating the sloped parts. I need to redecorate before its let out again, im going to use a fungacidal additive in the paint as an extra defense. Although like i mentioned the place has been relatively mould free except a small patch in the corner on the bathroom ceiling.